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-   -   what are these boards on top of joists? (http://www.diychatroom.com/f19/what-these-boards-top-joists-145025/)

dwoolver 05-27-2012 01:37 PM

what are these boards on top of joists?
 
2 Attachment(s)
Hi:

I'm planning to install a skylight over a small beakfast area in a 1960's ranch house in Northern California. The ceiling is suppoted by 2x4 joists 9ft long. There's a U-shaped channel built of a 1x6 and two 2x4s running down the center of the room on top of the joists (right photo). I'm not sure what the purpose of this structure is -- there are some wires attached to it part way like a running board, but it's more likely for structural reasons. There is a similar one running right down the center of the next room (left photo).

The reason I'm asking is that it's in the way of my skylight plans.

What is the purpose of this structure? Is it there to reinforce the ceiling?

What happens if I cut it to install the skylight? Can the headers for the skylight substitute as reinforcement?

What codes apply to this problem?

Thanks!

sixeightten 05-27-2012 02:49 PM

That roof looks very cobbled together. Are you sure your skylight will even work there? I see the valley in the one pic, and you want to stay clear of that.

dwoolver 05-27-2012 03:31 PM

skylight
 
Quote:

Originally Posted by sixeightten (Post 929837)
That roof looks very cobbled together. Are you sure your skylight will even work there? I see the valley in the one pic, and you want to stay clear of that.

The installation is in the right picture, not near the valley.

sixeightten 05-27-2012 03:34 PM

The 1x6 channel is probably what we call a stiffback. It helps to make the ceiling rigid. Cutting through it will ruin the rigidity. You will need some additional framing to carry the roof/ceiling framing at the skylight anyway, so you may be able to beef up the rest of the ceiling as well. This will need to be evaluated on site by a carpenter, contractor, engineer, or an architect.

kwikfishron 05-27-2012 03:55 PM

How big of a skylight are you thinking about? Maybe you can paint in some lines on your picture showing exactly where you want this to go.

Have you looked into Sun Tunnels? There a lot less intrusive on the structure.

Thurman 05-27-2012 04:44 PM

"Stiffback" in Ohio, "Strongback" in Georgia, serves the same purpose as stated. This stiffens the ceiling joists in both states.

dwoolver 05-27-2012 09:44 PM

size of skylight
 
Quote:

Originally Posted by kwikfishron (Post 929873)
How big of a skylight are you thinking about? Maybe you can paint in some lines on your picture showing exactly where you want this to go.

Have you looked into Sun Tunnels? There a lot less intrusive on the structure.


It's a Velux VSE M04, 30" wide, which will bring in a lot more light than a tube. At 30"wide I'll have to cut one rafter, but that's easily done within code.

dwoolver 05-27-2012 09:46 PM

stiffback
 
Quote:

Originally Posted by Thurman (Post 929895)
"Stiffback" in Ohio, "Strongback" in Georgia, serves the same purpose as stated. This stiffens the ceiling joists in both states.


... So I'll need to maintain stiffness when I put in the light tunnel through the ceiling. I'll need to understand why it was originally installed to be sure I acheive that purpose. Thanks.

joecaption 05-27-2012 09:58 PM

If I had to guess, that roof was framed so lightly with under sized lumber because org. there was a metal roof not shingles.
Since then someone added OSB and shingles without adding to the inside framing to support it so it's loaded way behond what it was built to support.
It should be fine to install a light that's the same or less then the spacing of the rafters, but I would never dare to start cutting what little you have to support that roof.
You could always add two smaller ones.

dwoolver 05-28-2012 12:03 PM

Quote:

Originally Posted by joecaption (Post 930099)
If I had to guess, that roof was framed so lightly with under sized lumber because org. there was a metal roof not shingles.
Since then someone added OSB and shingles without adding to the inside framing to support it so it's loaded way behond what it was built to support.
It should be fine to install a light that's the same or less then the spacing of the rafters, but I would never dare to start cutting what little you have to support that roof.
You could always add two smaller ones.

Thanks for your comment You are correct that it's not the original roof. The original was wood shakes, which left fragments all over the attic when the current shingle roof was put on over OSB. Some of the houses in this track still have the original shakes, surprisingly after nearly 50 years. From the looks of it I don't think the framing was modified at the time the new roof was put on. For example the purlins look original. I intend to keep the purlin in place, putting the skylight below it. I could double the rafters, as an extra measure. I'm more concerned about how to deal with the ceiling: 2x4s on 16" and that stiff back.

ddawg16 05-28-2012 06:22 PM

Your roof is so typical of how they did all the roofs in California during that time.....mine is built pretty much the same way.

I would not take out the channel....it could be as simple as a modified rafter tie....I had a bunch of wood in my attic that was there only to hold it all together while they framed it. As one old timer told me...they would put up the walls...get out the tape measure and level and start squaring up the house....then use 1x6's to hold it all in place while they put on the roof.

As I understand it, you want that skylight centered on where that channel is? Is there no way you can accpet it going to one side or the other?

One little suggestion.....you don't have to frame the tunnel for the skylight the same size as the skylight....nothing wrong with making it look like a funnel....this will actually increase the amount of light you project into the room.

If you dead set on having the skylight centered over the channel....then make the channel part of the tunnel for the skylight....just cover it with stained wood or drywall. Make it a bit wider and you can prop plants on it....I think that would look pretty good.


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